Here is one:
There wasn’t a place for people who wanted to write something more substantive than a tweet. Blogs, while better for long-form, required a certain savviness to get up-and-running. Successful ones required constant care and feeding and typically focussed on a single subject matter. New ones lacked an audience. He went on to say that people sometimes just have one thing to say about a subject, not something every day or week. This is what Medium would solve for. (source)
It’s from Ev Williams and I think it means Medium is really promising.
Though maybe Odeo seemed promising too? Apple kind of head them off at the pass though.